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Hack an Expensive LED Bulb to Fit (nearly) Anywhere!

Introduction: Hack an Expensive LED Bulb to Fit (nearly) Anywhere!

LED lights are modern marvels but are fitted into antiquated packages meant to be retrofitted into stone-age fixtures. Whose idea was it anyway to cram space age technology into a bulb invented 100 years ago?! My problem was replacing a dim, halogen bulb illuminating a ceiling fan. The new light had to be:

Much brighter than the existing 100W halogen bulb

Dimmable

Low profile to fit in the limited space behind the cover

Nothing was available off the shelf though Amazon once had a light kit that included LEDs fitted to a large thin disc made to be retrofitted into ceiling fans, though, even that was undimmable, and not likely to have been bright enough anyway.

So, I did what any unsatisfied consumer does when confronted with inferior solutions: I hacked it! Here's how and why I did what I did....

Step 1: Find and Break a Bulb... Option #1

For this option, I used a 240 watt equivalent LED bulb. It's a hefty, solidly built, and expensive bulb made for outdoor use. Big box stores have them for about $40. Let's get to the four main components of (any) pre-packaged LED lamp:

Heat Sink: All LEDs generate heat and this light generates quite a bit of it that has to be dissipated. In this case, the white aluminum housing acts as a heat sink, though a passive one.

Lens: The clear faceted plastic lens acts to focus the emitted light into a useful beam. I won't need it here, but you may wish to use yours, so, be careful when dismantling your lamp as this soft plastic scratches easily.

Driver: The real meat of an LED lamp is the sophisticated electronics that supplies clean, regulated power to the diode. In this case case, the driver has been potted with a soft, white, easily removable silicone epoxy.

LED: The small yellow circular film embedded in the center of the heat sink is the LED. Thermally conductive paste keeps it loosely glued to the head sink. This is the same kind of paste that help draw heat out of a computer's CPU and into it's surrounding heat sink.

Let's take this thing apart!

Use a thin flat screwdriver to release the concealer ring and reveal the holding screws behind it.

Remove the lens and set aside for re-use, if necessary.

Remove the next concealer plate around the LED.

Cut the supply wires to the LED leaving a bit of insulation on so that you can easily maintain polarity when re-wiring later

Unscrew the driver from the back of the heat sink/housing.

Step 2: Find and Break a Bulb... Option #2

In this option, I took a "wet location" 120W equivalent outdoor bulb apart. Unlike the bulb in option #1, prior, this bulb is glass enclosed, and about half the price.

The front face of the bulb has been glued to the glass housing and can't be removed without breaking it. Crack it carefully, then remove pieces with pliers. Wear gloves and eye protection!

Remove the rest of the housing. In this bulb, heat conducting paste lines the contact between the reflector and the glass housing, turning the housing itself into a heat sink, albeit a pretty ineffective one.

Unscrew the driver, cut the LED supply wires, and set the reflector aside.

Step 3: Unpot the Driver (Option #1)

I needed the driver to fit into a pretty tight space. You might not have the same limitation, in which case, you might not need to unpot the driver. You will, however, need to remove the screw base to access the line voltage supply wires.

The plastic lamp base needs to be scored so that it can be easily removed. I used a Dremel with a cut-off wheel and scored the plastic just deep enough to penetrate the plastic without damaging the underlying electronics.

Use a flat screwdriver to pry apart the plastic halves, then peel 'em apart like a banana!

Some part of the potting compound may be easily removed, like this one was; simply remove it gently....

The top part of the driver will require careful epoxy removal. Give this job to someone who likes to pick scabs. Use fine tweezers, or nut picks to gently remove the epoxy. Be patient and plan on 15-30 minutes for this job.

Once done, carefully inspect your work for any damage. Did you remember the polarity of the wiring at the line supply end?

Step 4: Unpot the Driver (Option #2)

The process for unpotting this driver isn't very different than that on the previous page:

Carefully score the plastic housing with a Dremel and cut-off wheel.

Gently peel off the housing material.

Carefully pry out the soft epoxy.

Check for damage.

Step 5: Modify Your Heat Sink

The heat sink is very important as it lengthens the lifetime of the LED by carrying heat away from the back of the diode. In many cases, the bulb housing does double duty as heat sink. If you remove it, you'll have to replace it with some other way to get heat off the back of the diode. Some high quality, small-profile bulbs come with an integrated cooling fan that blows heat off the diode. Again, the Dremel comes to the rescue:

Remove the LED from the heat sink.

Figure out some way to efficiently re-use whatever part of the existing heat sink you want. I tried a couple of different ways to modify the existing sink for my application until I finally decided that I really only wanted to use the LED holder without the surrounding materials.

The holder/sink must make intimate contact with the rest of your sink. I used an ordinary belt sander with 120 grit belt to remove excess aluminum from the back of this heat sink. Then, I polished it smooth with 400 grit waterproof sandpaper.

Once it has been polished smooth, coat it with thermal paste. It is now ready for installation of the other part of the heat sink.

A note about heat...

This light gets pretty hot. The housing does a good job of conducting heat away from the back of the LED, but that's as far as it goes: now that the housing is toasty hot, it counts on the surrounding air to move heat off of itself through convection and conduction, and, if there's a breeze or rain, advection. It's not a very efficient system as the housing also acts to heat up the driver, insulated snugly in its silicone cocoon. Now that you have liberated and separated all of these components, you should think about getting that heat off of the LED and keeping it away from the driver! Perhaps your new configuration will be more efficient than the original!

Step 6: Custom Re-Assembly

For this project, I retrofitted the LED and driver to an old halogen light fixture on the bottom of a ceiling fan. I didn't have to worry about heating this thing up any more than the old halogen bulb did. Importantly, the integrated dimmer switch worked perfectly with this new LED retrofit.

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7 Comments

...assuredly the designers did the best they could given cost and size limits, and then tested it thoroughly to make sure it would last a reasonably long life under expected conditions

Given time-to-market constraints, manufacturers design such products around well established performance and safety parameters and model various aesthetic permutations of the product "look" around those parameters.

Importantly, the manufacturer counts on the consumer replacing such a product long before their advertised (largely hypothetical) lifetime, allowing them considerable leeway in design and advertised promises. Given these points, one should have little confidence that manufacturers "thoroughly test" their integrated products and one should note that they largely rely on consumers to do their testing for them; the early generation of lousy LED products are a great case in point.

Nevertheless it's hard to quibble with your main point: if you want the modded product to run as long as the original, make cooling of the modification as efficient as the original. My own qualitative "touch test" of the modifications indicated that the steel mounting plates did a reasonable job keeping the LEDs within a similar range of temperatures as the original LED housing. A future temperature test using a remote thermal probe will better quantify temperature comparisons. As for this often repeated statement:

...statistically its lifetime will be reduced by 50% for every 10 degree Celsius increase in the chip temperatures.

I've yet to see how this squares with the newer generation of LED chips and the fact that there is still no approved method for testing lifetimes of consumer LED products....including the electronic components that drive these products.

The original cast aluminum housing of the LED bulb might not be super efficient at moving heat away from the LED module, but assuredly the designers did the best they could given cost and size limits, and then tested it thoroughly to make sure it would last a reasonably long life under expected conditions.

If modifying the heatsink and heatflow arrangements from what it was designed for, some critical factors are: airflow (does the glass cover allow any airflow or is this now a "sealed" fixture?), type of metal used as heatsink (steel is *much* poorer at conducting heat than aluminum is), and thickness of the metal where it meets other heatsink parts. If the aluminum gussets on the original aluminum housing were designed to be "heat flow highways", then a thin sheet of steel is a narrow alley in comparison. To extend the analogy, If the LED module is a city center in summer, think of a traffic jam of hot cars all trying to go over a few narrow bridges to get to the cooler countryside!

Excuse the funny analogy, my point is that the LED module *does* need to have a heatsink arrangement that's at least as efficient as the original bulb offers, just as the author noted. But this particular arrangement for heatsinking the LED module is very likely to be somewhat worse for the LEDs. It may not fail right away, but statistically its lifetime will be reduced by 50% for every 10 degree Celsius increase in the chip temperatures.

I want to be constructive and helpful, so I will suggest this: at least make a thick circle of aluminum plate as large as the punched steel piece from the fan. It will work better at moving heat than the thin steel piece alone. If air can still flow upwards through the bulb cavity on this fan, that is also a major help. For those interested in learning more about heat sink design, there are resources online. A good keyword to start with is "thermal resistance", as heat flow can be predicted using equations similar to Ohms law for electrical resistance.